Method of reducing kogation on heater of ink-jet recording head, ink-jet recording process, ink-jet recording apparatus, recording unit, and method for lengthening the life of recording head

ABSTRACT

Disclosed herein is a method of reducing kogation on the surface of a heater for applying thermal energy to an ink to eject the ink from an orifice in an ink-jet printer having a recording head equipped with the heater, wherein the heater has an outermost protective layer comprising a metal and/or a metal oxide, and the ink comprises (a) a coloring material, (b) a liquid medium, and (c) at least one selected from the group consisting of aldonic acid, γ-aldonolactone, δ-aldonolactone and aldonates.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method of reducing kogation on the surface of a heater for applying thermal energy to an ink, an ink-jet recording process, an ink-jet recording apparatus, a recording unit, and a method for lengthening the life of an ink-jet recording head.

[0003] 2. Related Background Art

[0004] Various systems have heretofore been proposed on printing using an ink-jet system. Among others, an ink-jet system (the so-called bubble-jet system) described in, for example, Japanese Patent Application Laid-Open No. 54-51837 or the like, in which an ink is ejected as ink droplets by the action of thermal energy, features that the formation of a high-density multi-nozzle in a recording head can be realized with very ease, high-quality images can be provided at high speed and very low cost, and printing can also be conducted on plain paper having no special coating layer. According to this system, a heater of a recording head is rapidly heated, thereby generating bubbles in a liquid on the heater to cause a rapid volumetric increase of the liquid. A droplet of the liquid is ejected from an nozzle of the recording head by the working force due to this rapid volumetric increase and applied to a recording medium, thereby conducting printing.

[0005] According to this system, however, a decomposition deposit (the so-called scorch) of an ink may be built up on the surface of the heater in some cases as the result that the heater of the recording head is repeatedly heated for ejecting the ink upon mass printing. In some cases, the build-up of the scorch may involve a problem that thermal energy cannot be effectively transferred from the heater to the ink, so that the quantity of the droplets ejected and the velocity of the droplets ejected are reduced compared with the initial printing, which adversely affects the quality of images formed. When it is intended to continuously achieve high-quality printing in this case, it is necessary to change the recording head. Such circumstances lead to increase in printing cost for users as a whole. Accordingly, achieving more reduction in kogation on the heater, which has a possibility of causing such circumstances, so as to more lengthen the life of the recording head is always an important technical problem to aim at a further improvement in the bubble-jet system.

[0006] For example, Japanese Patent Application Laid-Open No. 3-160070 has proposed an ink comprising an oxo anion. As examples of the oxo anion, are mentioned phosphates, polyphosphates, phosphoric esters, arsenates, molybdates, sulfates, sulfites and oxalates.

SUMMARY OF THE INVENTION

[0007] It is an object of the present invention to provide a method of more reducing kogation on the surface of a heater for applying thermal energy to an ink in a recording head to eject the ink from the recording head.

[0008] Another object of the present invention is to provide an ink-jet recording apparatus which permits higher-quality printing and the achievement of a more lengthened life of a recording head.

[0009] A further object of the present invention is to provide a recording unit which permits high-quality printing over a long period of time.

[0010] A still further object of the present invention is to provide a method for lengthening the life of a recording head to achieve further reduction in printing cost while providing high-quality prints.

[0011] The above objects can be achieve by the present invention described below.

[0012] According to the present invention, there is thus provided a method of reducing kogation on the surface of the outermost protective layer of a heater for applying thermal energy to an ink to eject the ink from an orifice in an ink-jet printer having a recording head equipped with the heater, wherein the outermost protective layer comprises a metal and/or a metal oxide, and the ink comprises (a) a coloring material, (b) a liquid medium, and (c) at least one selected from the group consisting of aldonic acid, γ-aldonolactone, δ-aldonolactone and aldonates.

[0013] According to this constitution, the kogation on the outermost protective layer of the heater can be extremely effectively reduced. The reason why such an effect is brought about by using such an ink is not clearly known. However, it is considered that at least one selected from the group consisting of aldonic acid, γ-aldonolactone, δ-aldonolactone and aldonates in the ink interacts with the metal and/or the metal oxide making up the outermost protective layer of the heater to prevent kogation or facilitate decomposition of scorch and separation of scorch from the heater surface.

[0014] When the metal contained in the outermost protective layer of the heater is tantalum, or the metal oxide is tantalum oxide, the effect becomes more noticeable. Supposing that the quantity of energy applied to the heater is Eop, and the threshold quantity of energy applied to the heater, which is required to eject the ink, is Eth, the kogation-preventing effect of the present invention becomes far excellent when the quantity of energy applied to the heater is preset in such a manner that Eop meets the relationship

1.10≦Eop/Eth≦1.50.

[0015] According to the present invention, there is also provided an ink-jet recording process comprising the step of applying thermal energy to an ink to eject the ink from an orifice, wherein the ink comprises (a) a coloring material, (b) a liquid medium, and (c) at least one selected from the group consisting of aldonic acid, γ-aldonolactone, δ-aldonolactone and aldonates.

[0016] According to the present invention, there is further provided an ink-jet recording apparatus comprising:

[0017] an ink container portion containing an ink,

[0018] an ink-jet recording head having a heater for applying thermal energy to the ink within an ink flow path, which is fed from the ink container portion, and

[0019] a means for applying a pulsed electric signal in response to recording information to the heater, wherein the heater has an outermost protective layer comprising a metal and/or a metal oxide, and the ink comprises (a) a coloring material, (b) a liquid medium, and (c) at least one selected from the group consisting of aldonic acid, γ-aldonolactone, δ-aldonolactone and aldonates.

[0020] According to the present invention, there is still further provided a recording unit comprising an ink container portion containing an ink, and an ink-jet recording head for ejecting the ink from an orifice by the action of thermal energy, wherein the ink-jet recording head is equipped with a heater for applying thermal energy to the ink, which has an outermost protective layer comprising a metal and/or a metal oxide, and the ink comprises (a) a coloring material, (b) a liquid medium, and (c) at least one selected from the group consisting of aldonic acid, γ-aldonolactone, δ-aldonolactone and aldonates.

[0021] According to the present invention, there is yet still further provided a method of lengthening the life of a recording head equipped with a heater for applying thermal energy to an ink, which is suitable for use in an ink-jet recording process comprising the step of applying thermal energy to an ink to eject the ink from an orifice, the method comprising providing an outermost protective layer comprising at least one of a metal and a metal oxide on the heater, and using, as the ink, an ink comprising (a) a coloring material, (b) a liquid medium, and (c) at least one selected from the group consisting of aldonic acid, γ-aldonolactone, δ-aldonolactone and aldonates.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1 is a longitudinal cross-sectional view of an exemplary head of an ink-jet recording apparatus.

[0023]FIG. 2 is a transverse cross-sectional view of the head of the ink-jet recording apparatus.

[0024]FIG. 3 is a perspective view of the appearance of a multi-head which is an array of such heads as shown in FIG. 1.

[0025]FIG. 4 is a schematic perspective view illustrating an exemplary ink-jet recording apparatus.

[0026]FIG. 5 is a longitudinal cross-sectional view illustrating an exemplary ink cartridge.

[0027]FIG. 6 is a perspective view illustrating an exemplary recording unit.

[0028]FIG. 7 diagrammatically illustrates driving pulses of an On-Demand type multi-recording head.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] The present invention will hereinafter be described in more detail by the preferred embodiments.

[0030] (Aldonic Acid, γ-aldonolactone, δ-aldonolactone and Aldonates)

[0031] Aldonic acid, γ-aldonolactone, δ-aldonolactone and aldonates will be first described. The present inventors have carried out an extensive investigation as to a method of reducing kogation on a heater of an ink-jet recording head in an ink-jet recording method in which an ink is ejected as ink droplets by the action of thermal energy. As a result, it has been found that when at least one selected from the group consisting of aldonic acid, γ-aldonolactone, δ-aldonolactone and aldonates is contained in the ink, kogation can be very effectively reduced, thus leading to completion of the present invention.

[0032] Aldonic acid is a polyoxycarboxylic acid corresponding to a product obtained by oxidizing the aldehyde group of an aldose into a carboxyl group and is represented by the general formula

HOCH₂(C*HOH)_(n)COOH

[0033] wherein n is an integer of 0 or larger, and C* denotes an asymmetric carbon atom.

[0034] Since the aldonic acid has an asymmetric carbon atom as indicated by the above general formula, many optical isomers exist. It is said that an aldonic acid having at least 5 carbon atoms (n in the general formula is 3 or larger) is seldom present by itself in an aqueous solution, and a part of the aldonic acid generally forms a lactone with the hydroxyl group located at its γ or δ position to become γ-aldonolactone or δ-aldonolactone, and so the aldonic acid is present as an equilibrium mixture of the three compounds of aldonic acid, γ-aldonolactone and δ-aldonolactone, in the aqueous solution. It is also said that an aldonic acid having 4 carbon atoms (n in the general formula is 2) is seldom present by itself in an aqueous solution, and a part of the aldonic acid generally forms a lactone with the hydroxyl group located at its γ position to become γ-aldonolactone, and so the aldonic acid is present as an equilibrium mixture of the two compounds of aldonic acid and γ-aldonolactone, in the aqueous solution.

[0035] Aldonic acid is classified by the number of carbon atoms, and an aldonic acid having 4 carbon atoms (n in the general formula is 2) is generally designated as tetronic acid, an aldonic acid having 5 carbon atoms (n in the general formula is 3) as pentonic acid, and an aldonic acid having 6 carbon atoms (n in the general formula is 4) as hexonic acid. Specific examples of aldonic acid include glycolic acid (another name: hydroxyacetic acid) having 2 carbon atoms (n in the general formula is 0); glyceric acid having 3 carbon atoms (n in the general formula is 1); erythronic acid and threonic acid each having 4 carbon atoms (n in the general formula is 2); ribonic acid, arabonic acid, xylonic acid and lyxonic acid each having 5 carbon atoms (n in the general formula is 3); gluconic acid, allonic acid, altronic acid, mannonic acid, gulonic acid, idonic acid, galactonic acid and talonic acid having 6 carbon atoms (n in the general formula is 4); and glucoheptonic acid having 7 carbon atoms (n in the general formula is 4). Respective D-forms, L-forms and DL-forms exist in these compounds.

[0036] Gluconic acid which is particularly preferred among the aldonic acids according to the present invention will be described. It is said that gluconic acid is seldom present by itself in an aqueous solution, and a part of the aldonic acid generally forms a lactone with the hydroxyl group located at its γ or δ position to become γ-gluconolactone or δ-gluconolactone, and so the aldonic acid is present as an equilibrium mixture of the three compounds of gluconic acid, γ-gluconolactone and δ-gluconolactone, in the aqueous solution. D-Form, L-form and DL-form exist in gluconic acid, and any compound may be used. However, D-gluconic acid of the D-form is generally easily available. As optical isomers of gluconic acid, allonic acid, altronic acid, mannonic acid, gulonic acid, idonic acid, galactonic acid and talonic acid exist. Since these compounds show a nature like gluconic acid, they may also be used.

[0037] Examples of salts of gluconic acid include lithium gluconate, sodium gluconate, potassium gluconate, magnesium gluconate, calcium gluconate, barium gluconate, iron(II) gluconate and copper(II) gluconate. Of these, lithium gluconate, sodium gluconate and potassium gluconate are preferably used. It goes without saying that these compounds may be used either singly or in any combination thereof.

[0038] The total content of at least one compound selected from the group consisting of gluconic acid, γ-gluconolactone, δ-gluconolactone and gluconate is 0.005 to 20% by weight, preferably 0.05 to 12% by weight, based on the total weight of the ink. If the total content is lower than 0.005% by weight, the kogation-reducing effect of such a component is not brought about. If the total content is higher than 20% by weight, it can no longer be expected that the effect is further enhanced. Therefore, such a high content is disadvantageous from the viewpoint of cost.

[0039] (Coloring Material)

[0040] The coloring material used in the present invention will be described. As the coloring material, a dye or pigment is preferably used.

[0041] (Dye)

[0042] As the dye, all dyes such as direct dyes, acid dyes, basic dyes and disperse dyes may be used. Specific examples thereof include:

[0043] C.I. Direct Black 4, 9, 11, 17, 19, 22, 32, 80, 151, 154, 168, 171, 194 and 195;

[0044] C.I. Direct Blue 1, 2, 6, 8, 22, 34, 70, 71, 76, 78, 86, 142, 199, 200, 201, 202, 203, 207, 218, 236 and 287;

[0045] C.I. Direct Red 1, 2, 4, 8, 9, 11, 13, 15, 20, 28, 31, 33, 37, 39, 51, 59, 62, 63, 73, 75, 80, 81, 83, 87, 90, 94, 95, 99, 101, 110, 189, 225 and 227;

[0046] C.I. Direct Yellow 1, 2, 4, 8, 11, 12, 26, 27, 28, 33, 34, 41, 44, 48, 86, 87, 88, 132, 135, 142 and 144;

[0047] C.I. Food Black 1 and 2;

[0048] C.I. Acid Black 1, 2, 7, 16, 24, 26, 28, 31, 48, 52, 63, 107, 112, 118, 119, 121, 172, 194 and 208;

[0049] C.I. Acid Blue 1, 7, 9, 15, 22, 23, 27, 29, 40, 43, 55, 59, 62, 78, 80, 81, 90, 102, 104, 111, 185 and 254;

[0050] C.I. Acid Red 1, 4, 8, 13, 14, 15, 18, 21, 26, 35, 37, 52, 249, 257 and 289;

[0051] C.I. Acid Yellow 1, 3, 4, 7, 11, 12, 13, 14, 19, 23, 25, 34, 38, 41, 42, 44, 53, 55, 61, 71, 76 and 79;

[0052] C.I. Reactive Blue 1, 2, 3, 4, 5, 7, 8, 9, 13, 14, 15, 17, 18, 19, 20, 21, 25, 26, 27, 28, 29, 31, 32, 33, 34, 37, 38, 39, 40, 41, 43, 44 and 46;

[0053] C.I. Reactive Red 1, 2, 3, 4, 5, 6, 7, 8, 11, 12, 13, 15, 16, 17, 19, 20, 21, 22, 23, 24, 28, 29, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 45, 46, 49, 50, 58, 59, 63, 64 and 180;

[0054] C.I. Reactive Yellow 1, 2, 3, 4, 6, 7, 11, 12, 13, 14, 15, 16, 17, 18, 22, 23, 24, 25, 26, 27, 37 and 42;

[0055] C.I. Reactive Black 1, 3, 4, 5, 6, 8, 9, 10, 12, 13, 14 and 18; and

[0056] Projet Fast Cyan 2 (product of Zeneca Co.), Projet Fast Magenta 2 (product of Zeneca Co.), Projet Fast Yellow 2 (product of Zeneca Co.) and Projet Fast Black 2 (product of Zeneca Co.). However, the dyes used in the present invention are not limited to these dyes.

[0057] (Pigment)

[0058] As the pigment, all pigments such as inorganic pigments and organic pigments may be used.

[0059] Specific examples thereof include:

[0060] Carbon Black;

[0061] C.I. Pigment Yellow 1, 2, 3, 12, 13, 14, 16, 17, 73, 74, 75, 83, 93, 95, 97, 98, 114, 128, 129, 151, 154 and 195; C.I. Pigment Red 5, 7, 12, 48(Ca), 48(Mn), 57(Ca), 57:1, 57(Sr), 112, 122, 123, 168, 184 and 202;

[0062] C.I. Pigment Blue 1, 2, 3, 15:3, 15:34, 16, 22 and 60; and

[0063] C.I. Vat Blue 4 and 6.

[0064] (Dispersing Agent)

[0065] When these pigments are used, it is preferable to use dispersing agents for stably dispersing such a pigment in an ink. The dispersing agents includes polymeric dispersing agents and surfactant type dispersing agents. Specific examples of the polymeric dispersing agents include polyacrylates, salts of styrene-acrylic acid copolymers, salts of styrene-methacrylic acid copolymers, salts of styrene-acrylic acid-acrylic ester terpolymers, salts of styrene-maleic acid copolymers, salts of acrylic ester-maleic acid copolymers, salts of styrene-methacrylsulfonic acid copolymers, salts of vinylnaphthalene-maleic acid copolymers, salts of β-naphthalenesulfonic acid-formalin condensates, polyvinylpyrrolidone, polyethylene glycol and polyvinyl alcohol. These polymers preferably have a weight average molecular weight ranging from 1,000 to 30,000 and an acid value ranging from 100 to 430. Examples of the surfactant type dispersing agents include lauryl benzenesulfonates, lauryl sulfonates, lauryl benzenecarboxylates, lauryl naphthalenesulfonates, aliphatic amine salts and polyethylene oxide condensates. The amount of these dispersing agents used is preferably within a range of from 10:5 to 10:0.5 in terms of a ratio of the weight of the pigment to the weight of the dispersing agent.

[0066] (Self-dispersing CB)

[0067] Carbon black capable of self-dispersing, which is obtained by introducing a water-soluble group into the surface of carbon black as described in Japanese Patent Application Laid-Open Nos. 5-186704 and 8-3498, may also be used. No dispersing agent may be used when the self-dispersing carbon black is used.

[0068] These dyes and pigments may be used either singly or in any combination thereof. The concentration of these dyes and pigments is generally selected suitably from a range of from 0.1 to 20% by weight based on the total weight of the ink.

[0069] (Aqueous Medium)

[0070] The aqueous medium used in the present invention will now be described. As the liquid medium, it is preferable to use water and a water-soluble organic solvent in combination.

[0071] With respect to the water used in the present invention, it is desirable to use deionized water instead of tap water containing various ions. The content of water is preferably within a range of from 35 to 96% by weight based on the total weight of the ink.

[0072] The water-soluble organic solvent is used for adjusting the viscosity of an ink to a suitable viscosity preferred from the viewpoint of practical use, and for slowing the drying speed of the ink or enhancing the solubility of the coloring material to prevent clogging at the nozzle in a recording head. Specific examples of the water-soluble organic solvent include alkyl alcohols having 1 to 5 carbon atoms, such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, isobutyl alcohol and n-pentanol; amides such as dimethylformamide and dimethylacetamide; ketones and ketone alcohols such as acetone and diacetone alcohol; ethers such as tetrahydrofuran and dioxane; oxyethylene or oxypropylene copolymers such as diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, polyethylene glycol and polypropylene glycol; alkylene glycols the alkylene moiety of which has 2 to 6 carbon atoms, such as ethylene glycol, propylene glycol, trimethylene glycol and triethylene glycol; 1,2,6-hexanetriol; glycerol; trimethylolethane and trimethylolpropane; lower alkyl ethers such as glycerin, trimethylolethane, trimethylolpropane, ethylene glycol monomethyl (or monoethyl) ether, diethylene glycol monomethyl (or monoethyl) ether and triethylene glycol monomethyl (or monoethyl) ether; lower dialkyl ethers of polyhydric alcohols, such as triethylene glycol dimethyl (or diethyl) ether and tetraethylene glycol dimethyl (or diethyl) ether; alkanolamines such as monoethanolamine, diethanolamine and triethanolamine; sulfolane; N-methyl-2-pyrrolidone; 2-pyrrolidone; and 1,3-dimethyl-2-imidazolidinone. Such water-soluble organic solvents as mentioned above may be used either singly or in any combination thereof.

[0073] (Additives)

[0074] In order to keep the pH value of the ink according to the present invention constant to stabilize the solubility of the dye or the dispersibility of the pigment in the ink, a pH adjuster may be contained in the ink. Specific examples of the pH adjuster include hydroxides such as lithium hydroxide, sodium hydroxide, potassium hydroxide and ammonium hydroxide; acids such as sulfuric acid and hydrochloric acid; salts of these hydroxides and acids; sulfates such as lithium sulfate, sodium sulfate potassium sulfate and ammonium sulfate; carbonates such as lithium carbonate, sodium carbonate, sodium hydrogencarbonate, potassium carbonate, potassium hydrogencarbonate, sodium potassium carbonate, ammonium carbonate and ammonium hydrogencarbonate; phosphates such as lithium phosphate, monosodium phosphate, disodium phosphate, trisodium phosphate, monopotassium phosphate, dipotassium phosphate, tripotassium phosphate, monoammonium phosphate, diammonium phosphate and triammonium phosphate; and acetates such as lithium acetate, sodium acetate, potassium acetate and ammonium acetate.

[0075] These salts may be added singly to the ink. However, it is preferable to use at least two of these salts in combination. The total amount of these salts added is preferably 0.1 to 10% by weight, more preferably 1 to 8% by weight. If the amount added is less than 0.1% by weight, it is difficult to keep the pH of the ink constant, so that little effect is exerted on the solution stability of the hydrophilic dye contained in the ink. On the other hand, if the amount is greater than 10% by weight, crystals of these salts are deposited to cause clogging of nozzles, and the like. It is not rather preferable to add the pH adjuster in such a large amount.

[0076] To the inks according to the present invention, the conventionally known various general additives, for example, viscosity modifiers, mildewproofing agents, antiseptics, antioxidants, antifoaming agents, surfactants and agents for preventing the drying of nozzles, such as urea, may be added in suitable combination in addition to the above-described components, as needed.

[0077] (Physical Properties)

[0078] With respect to the physical properties of the inks according to the present invention, the pH is preferably within a range of from 3 to 12, more preferably 4 to 10, the surface tension is preferably within a range of from 10 to 60 dyn/cm, more preferably 15 to 50 dyn/cm, and the viscosity is preferably within a range of from 1 to 30 cP, more preferably from 1 to 10 cP, all, as measured at about 25° C.

[0079] (Recording Method)

[0080] A recording method suitable for use in recording with the inks according to the present invention is an ink-jet recording method in which thermal energy corresponding to recording signals is applied to an ink within a recording head, and ink droplets are generated by the thermal energy. Such recording apparatus as the inks according to the present invention are suitably used will hereinafter be described with reference to the drawings.

[0081] An example of the construction of a head, which is a main component of an ink-jet recording apparatus making good use of thermal energy is first illustrated in FIGS. 1 and 2. FIG. 1 is a cross-sectional view of a head 13 taken along the flow path of ink, and FIG. 2 is a cross-sectional view taken along line 2-2 in FIG. 1. The head 13 is formed by bonding a glass, ceramic, silicon, polysulfone or plastic plate or the like having a flow path (nozzle) 14 through which an ink is passed, to a heating substrate 15. The heating substrate 15 is composed of a protective layer 16-1 made of silicon oxide, silicon nitride, silicon carbide or the like, an outermost protective layer 16-2 formed of a metal or metal oxide, preferably, tantalum or tantalum oxide, or the like, electrodes 17-1 and 17-2 formed of aluminum, gold, aluminum-copper alloy or the like, a heating resistor layer 18 formed of a high-melting material such as, hafnium boride, tantalum nitride or tantalum aluminum, a heat accumulating layer 19 formed of silicon oxide, aluminum oxide or the like, and a substrate 20 made of silicon, aluminum, aluminum nitride or the like having a good heat radiating property.

[0082] Now, upon application of pulsed electric signals to the electrodes 17-1 and 17-2 of the head 13, the heating substrate 15 rapidly generates heat at the region (heater) shown by “n” to form bubbles in an ink 21 which is in contact with this region. A meniscus 23 of the ink is projected by the pressure thus produced, and the ink 21 is ejected in the form of ink droplets 24 from an ejection orifice 22 through the nozzle 14 of the head 13 toward a recording medium 25. FIG. 3 illustrates an appearance of a multi-head composed of an array of a number of heads as shown in FIG. 1. The multi-head is formed by closely bonding a glass plate 27 having a number of nozzles 26 to a heating head 28 similar to that described in FIG. 1.

[0083] (Quantity of Energy Applied to Heater)

[0084] Energy applied to the heater will now be described. Supposing that critical energy that a bubble-jet head may barely conduct ejection is Eth, and energy actually applied is Eop, a ratio (Eop/Eth) between them will be expressed as r. More specifically, supposing that a width of a pulse applied to the bubble-jet head is P (when a plurality of pulses are applied in portions, it means the total width thereof), voltage applied is V, and resistance of the heater is R, energy E applied can be expressed as

E=P×V ² /R  (1).

[0085] At this time, when critical energy that the bubble-jet head may barely conduct ejection is Eth, and energy actually applied upon driving is Eop, the r value is given by

r=Eop/Eth  (2).

[0086] Examples of a method for finding the r value from the driving conditions of the bubble-jet head include the following two methods.

[0087] (Method 1) Case where a Pulse Width is Fixed:

[0088] Proper voltage with which the bubble-jet head can conduct ejection in a given pulse width is first found to drive the head. The voltage is then gradually lowered to find voltage that the ejection is stopped. The lowest voltage that ejection can be conducted right before the ejection is stopped is regarded as Vth. When voltage actually used upon driving is regarded as Vop, the r value can be found by

r=(Vop/Vth)².

[0089] (Method 2) Case where Voltage is Fixed:

[0090] A proper pulse width with which the bubble-jet head can conduct ejection in a given voltage is first found to drive the head. The pulse width is then gradually shortened to find a pulse width that the ejection is stopped. The shortest pulse width that ejection can be conducted right before the ejection is stopped is regarded as Pth. When a pulse width actually used upon driving is regarded as Pop, the r value can be found by

r=Pop/Pth.

[0091] Incidentally, the voltage value as referred to herein is voltage actually applied to a heater portion for heating the BJ heater. The voltage applied from the outside of the head may be lowered by contacts, resistance of wiring, and the like. When the Vth and Vop are measured from the outside of the head, however, measurement is conducted with these voltage variations included in both values. Therefore, an error is small even when these measured values are directly used to calculate the r value so far as the voltage variations are not very large, and the use of the calculated value as the r value has no trouble.

[0092] Attention must be paid to the fact that when recording is conducted by an actual printer, voltage to one heater may possibly be affected by this to vary it because plural heaters are driven.

[0093] From the above equations (1) and (2), the square of V seems to be inversely proportional to P in the same r value. In fact, the square of V is not simply related to p because of a electrical problem that a pulse shape does not become a rectangle, a thermal problem that heat diffusion about the heater is different when pulse shape varies, and a problem characteristic of bubble jet that heat flux from the heater to the ink is different to change a bubbling state when voltage varies. Accordingly, the above methods 1 and 2 must be treated independently of each other, and one must take care that an error is produced when one value is converted into the other value by calculation. In this specification, the values found in accordance with Method 1 will be adopted as r values unless expressly noted.

[0094] In order to stably eject an ink, it is general to drive a recording head under the r value of about 1.12 to 1.96. However, when thermal energy is applied to an ink comprising at least one selected from the group consisting of aldonic acid, γ-aldonolactone, δ-aldonolactone and aldonates to eject it from a recording head, it is preferred that the recording head be driven under an r value within the prescribed range, specifically, from 1.10 to 1.50 in that kogation on a heater can be prevented, and in its turn the life of the recording head can be more lengthened. The reason why the kogation can be particularly effectively prevented within this range, and the life of the recording head can be lengthened is not clearly known. It is however considered that it is prevented to excessively raise the surface temperature of the heater by supplying the heater with energy in excess, and no excessive corrosion of the metal by aldonic acid, γ-aldonolactone, δ-aldonolactone and aldonates occurs.

[0095]FIG. 4 illustrates an example of an ink-jet recording apparatus in which such a head as described above has been incorporated. In FIG. 4, reference numeral 61 designates a blade serving as a wiping member, one end of which is a stationary end held by a blade-holding member to form a cantilever. The blade 61 is provided at a position adjacent to a region in which a recording head 65 operates, and in this embodiment, is held in such a form that it protrudes into the course through which the recording head 65 is moved.

[0096] Reference numeral 62 indicates a cap for the face of ejection openings of the recording head 65, which is provided at a home position adjacent to the blade 61, and is so constructed that it moves in a direction perpendicular to a direction in which the recording head 65 is moved, and comes into contact with the face of the ejection openings to cap it. Reference numeral 63 denotes an ink absorbing member provided adjoiningly to the blade 61 and, similar to the blade 61, held in such a form that it protrudes into the course through which the recording head 65 is moved. The above-described blade 61, cap 62 and ink absorbing member 63 constitute an ejection-recovery portion 64, where the blade 61 and ink absorbing member 63 remove water, dust and/or the like from the face of the ink-ejecting openings.

[0097] Reference numeral 65 designates the recording head having an ejection-energy-generating means and serving to eject the ink onto a recording medium set in an opposing relation to the ejection opening face provided with the ejection openings to conduct recording. Reference numeral 66 indicates a carriage on which the recording head 65 is mounted so that the recording head 65 can be moved. The carriage 66 is slidably interlocked with a guide rod 67 and is connected (not illustrated) at its part to a belt 69 driven by a motor 68 Thus, the carriage 66 can be moved along the guide rod 67 and hence, the recording head 65 can be moved from a recording region to a region adjacent thereto.

[0098] Reference numerals 51 and 52 denote a feeding part from which the recording medium is inserted, and feed rollers driven by a motor (not illustrated), respectively. With such a construction, the recording medium is fed to the position opposite to the ejection opening face of the recording head 65, and discharged from a discharge section provided with discharge rollers 53 with the progress of recording. In the above construction, the cap 62 in the head recovery portion 64 is receded from the path of motion of the recording head 65 when the recording head 65 is returned to its home position, for example, after completion of recording, and the blade 61 remains protruded into the path of motion. As a result, the ejection opening face of the recording head 65 is wiped.

[0099] When the cap 62 comes into contact with the ejection opening face of the recording head 65 to cap it, the cap 62 is moved so as to protrude into the path of motion of the recording head 65. When the recording head 65 is moved from its home position to the position at which recording is started, the cap 62 and the blade 61 are at the same positions as the positions for the wiping as described above. As a result, the ejection opening face of the recording head 65 is also wiped at the time of this movement. The above movement of the recording head 65 to its home position is made not only when the recording is completed or the recording head 65 is recovered for ejection, but also when the recording head 65 is moved between recording regions for the purpose of recording, during which it is moved to the home position adjacent to each recording region at given intervals, where the ejection opening face is wiped in accordance with this movement.

[0100] FIG.5 illustrates an exemplary ink cartridge 45 in which an ink to be fed to a recording head through an ink-feeding member, for example, a tube is contained. Here, a member 40 making up a part of the ink cartridge 45 is an ink container portion containing the ink to be fed, as exemplified by a bag for the ink. One end thereof is provided with a stopper 42 made of rubber. A needle (not illustrated) may be inserted into this stopper 42 so that the ink in the bag 40 for the ink can be fed to the head. Reference numeral 44 indicates an absorbing member for receiving a waste ink. It is preferred that the ink container portion 40 be formed of a polyolefin, in particular, polyethylene, at its surface with which the ink comes into contact.

[0101] The ink-jet recording apparatus used in the present invention are not limited to the apparatus as described above in which the head and the ink cartridge are separately provided. Therefore, a device in which these members are integrally formed as shown in FIG. 6 can also be preferably used. In FIG. 6, reference numeral 70 designates a recording unit, in the interior of which an ink container portion containing an ink, for example, an ink absorbing member, is contained. The recording unit 70 is so constructed that the ink in such an ink absorbing member is ejected in the form of ink droplets through a head 71 having a plurality of orifices. In the present invention, polyurethane is preferably used as a material for the ink absorbing member. The ink container portion may be constructed without using the ink absorbing member by a bag for the ink in the interior of which a spring or the like is provided. Reference numeral 72 indicates an air passage for communicating the interior of the recording unit 70 with the atmosphere. This recording unit 70 is used in place of the recording head 65 shown in FIG. 4, and is detachably installed on the carriage 66.

[0102] As described above, according to the present invention, there are provided inks which can lengthen the life of a recording head by reducing kogation on a heater of the recording head when they are used in ink-jet recording making good use of thermal energy, a method for lengthening the life of the recording head by reducing kogation on the heater of the recording head, and ink-jet recording process and ink-jet recording apparatus using such inks.

[0103] The present invention will hereinafter be described more specifically by the following Examples and Comparative Examples. However, the present invention is not limited to the following examples so far as it does not exceed the subject matter thereof. Incidentally, all designations of “part” or “parts” and “%” as will be used in the following examples mean part or parts by weight and % by weight unless expressly noted.

EXAMPLES 1 TO 3

[0104] and

Comparative Examples 1 to 4

[0105] The following respective components were mixed and thoroughly stirred into solutions. The resultant solutions were then filtered under pressure through a microfilter (product of Fuji Photo Film Co., Ltd.) having a pore size of 0.2 μm, thereby preparing an ink according to Example A, and an ink according to Comparative Example A, in which sodium gluconate was removed from the ink of Example A.

[0106] Ink composition of Example A: Projet Fast Black 2 (product of 2 parts Zeneca Co.) Diethylene glycol 10 parts Sodium gluconate 2 parts Sodium hydroxide 0.1 parts Water 85.9 parts.

[0107] Ink composition of Comparative Example A: Projet Fast Black 2 (product of 2 parts Zeneca Co.) Diethylene glycol 10 parts Sodium hydroxide 0.1 parts Water 87.9 parts.

[0108] [Evaluation 1]

[0109] The ink of Example A was used to conduct the following evaluation by means of an ink-jet recording apparatus having an On-Demand type multi-recording head (BC-02, trade name, manufactured by Canon Inc.; the outermost protective layer on a heater is formed of tantalum and tantalum oxide) which ejects an ink by applying thermal energy in response to recording signals to the ink. In the evaluation, Vth (critical voltage that the recording head may barely conduct ejection) was actually measured at a pulse width of 1.1 μs (On)+3.0 μs (Off)+3.2 μs (On) as illustrated in FIG. 7, and a driving frequency of 6250 Hz, and the evaluation was conducted at Vop (driving voltage) corresponding to an r value of 1.39 to regard it as EXAMPLE 1. Incidentally, Vop (driving voltage) was calculated out in accordance with the equation

Vop={square root}{square root over (r)}×Vth.

[0110] Using the ink of Example A, the same evaluation was conducted at Vop (driving voltage) corresponding to an r value of 1.10 to regard it as EXAMPLE 2, while the same evaluation was conducted at Vop (driving voltage) corresponding to an r value of 1.48 to regard it as EXAMPLE 3.

[0111] Further, the same evaluation was conducted at Vop (driving voltage) corresponding to an r value of 1.56 to regard it as COMPARATIVE EXAMPLE 1, the same evaluation was conducted at Vop (driving voltage) corresponding to an r value of 1.61 to regard it as COMPARATIVE EXAMPLE 2, and the same evaluation was conducted at Vop (driving voltage) corresponding to an r value of 1.69 to regard it as COMPARATIVE EXAMPLE 3.

[0112] Further, using the ink of Comparative Example A, the same evaluation was conducted at Vop (driving voltage) corresponding to an r value of 1.39 to regard it as COMPARATIVE EXAMPLE 4. The results are shown in Table 1.

[0113] Ejection Durability:

[0114] Continuous ejection was conducted by the above-described apparatus under the above-described respective driving conditions to collect a droplet ejected from the recording head every 1×10⁶ droplets in a container and weigh it by an electronic balance. An average quantity in 1×10⁶ droplets ejected was calculated from an increment in the weight of the container. The continuous ejection was conducted up to 1×10⁸ droplets to conduct the evaluation in accordance with the following standard.

[0115] A: An average quantity of droplets ejected between the 9.9×10⁷-th droplet and the 1×10⁸-th droplet was at least 90% of an average quantity of droplets ejected between 0 to 1×10⁶-th droplet;

[0116] B: An average quantity of droplets ejected between the 9.9×10⁷-th droplet and the 1×10⁸-th droplet was not lower than 70%, but lower than 90% of an average quantity of droplets ejected between 0 to 1×10⁶-th droplet;

[0117] C: An average quantity of droplets ejected between the 9.9×10⁷-th droplet and the 1×10⁸-th droplet was lower than 70% of an average quantity of droplets ejected between 0 to 1×10⁶-th droplet;

[0118] D: Led into a failure to eject in the course.

[0119] Degree of Kogation:

[0120] The recording head of the recording apparatus used in the ejection durability test was disassembled after completion of the evaluation to observe the surface of the heater in the nozzle used in the ejection durability test through an optical microscope (400 magnifications), thereby evaluating the degree of kogation in accordance with the following standard:

[0121] A: Kogation was scarcely observed;

[0122] B: Kogation was slightly observed, but no practical problem was caused;

[0123] C: Kogation was observed to a great extent;

[0124] D: Kogation was observed to a very great extent. TABLE 1 Type of aldonic acid Vth Vop Ejection Degree of Content (V) r value (V) durability kogation Ex. 1 Sodium gluconate 20.9 1.39 24.6 A A 2 parts EX. 2 Sodium gluconate 20.8 1.10 21.8 A A 2 parts Ex. 3 Sodium gluconate 21.0 1.48 25.5 A B 2 parts Comp. Sodium gluconate 20.9 1.56 26.1 C B Ex. 1 2 parts Comp. Sodium gluconate 20.7 1.61 26.3 D C Ex. 2 2 parts Comp. Sodium gluconate 21.2 1.69 27.6 D D Ex. 3 2 parts Comp. Not added 20.9 1.39 24.6 C C Ex. 4

EXAMPLES 4 TO 24

[0125] and

Comparative Examples 5 to 18

[0126] The following respective components were mixed and thoroughly stirred into solutions. The resultant solutions were then filtered under pressure through a microfilter (product of Fuji Photo Film Co., Ltd.) having a pore size of 0.2 μm, thereby preparing inks according to EXAMPLEs 4 to 24, and inks according to COMPARATIVE EXAMPLEs 5 to 18.

[0127] Ink composition of EXAMPLE 4: Projet Fast Black 2 (product of 2 parts Zeneca Co.) Diethylene glycol 10 parts Sodium glycolate 3 parts Water 85 parts.

[0128] Ink composition of EXAMPLE 5: Projet Fast Black 2 (product of 2 parts Zeneca Co.) Diethylene glycol 10 parts 40% aqueous solution of 4 parts DL-glyceric acid Sodium hydroxide 0.6 parts Water 83.4 parts.

[0129] Ink composition of EXAMPLE 6: Projet Fast Black 2 (product of 2 parts Zeneca Co.) Diethylene glycol 10 parts D-Erythronolactone 2 parts Sodium hydroxide 0.5 parts Water 85.5 parts.

[0130] Ink composition of EXAMPLE 7: Projet Fast Black 2 (product of 2 parts Zeneca Co.) Diethylene glycol 10 parts δ-Ribonolactone 2 parts Sodium hydroxide 0.5 parts Water 85.5 parts.

[0131] Ink composition of EXAMPLE 8: Projet Fast Black 2 (product of 2 parts Zeneca Co.) Diethylene glycol 10 parts γ-D-Galactonolactone 2 parts Sodium hydroxide 0.4 parts Water 85.6 parts.

[0132] Ink composition of EXAMPLE 9: Projet Fast Black 2 (product of 2 parts Zeneca Co.) Diethylene glycol 10 parts δ-Gluconolactone 2 parts Sodium hydroxide 0.5 parts Water 85.5 parts.

[0133] Ink composition of EXAMPLE 10: Projet Fast Black 2 (product of 2 parts Zeneca Co.) Diethylene glycol 10 parts 50% aqueous solution of 4 parts gluconic acid Lithium hydroxide monohydrate 0.4 parts Water 83.6 parts.

[0134] Ink composition of EXAMPLE 11: Projet Fast Black 2 (product of 2 parts Zeneca Co.) Diethylene glycol 10 parts Sodium glucoheptonate 2 parts Water 86 parts.

[0135] Ink composition of EXAMPLE 12: Projet Fast Yellow 2 (product of 3 parts Zeneca Co.) Diethylene glycol 10 parts Sodium gluconate 2 parts Water 85 parts.

[0136] Ink composition of EXAMPLE 13: Projet Fast Magenta 2 (product of 3 parts Zeneca Co.) Diethylene glycol 10 parts Sodium gluconate 2 parts Water 85 parts.

[0137] Ink composition of EXAMPLE 14: Projet Fast Cyan 2 (product of 4 parts Zeneca Co.) Diethylene glycol 10 parts Sodium gluconate 2 parts Water 84 parts.

[0138] Ink composition of EXAMPLE 15: C.I. Food Black 2 3 parts Glycerol 5 parts Ethylene glycol 10 parts 2-Propanol 3 parts Sodium gluconate 0.5 parts Water 78.5 parts.

[0139] Ink composition of EXAMPLE 16: C.I. Acid Yellow 23 2 parts Glycerol 5 parts Ethylene glycol 10 parts 2-Propanol 3 parts Magnesium gluconate 3 parts Sodium hydroxide 0.1 parts Water 75.9 parts.

[0140] Ink composition of EXAMPLE 17: C.I. Reactive Red 180 2.5 parts Glycerol 5 parts Ethylene glycol 10 parts 2-Propanol 3 parts Sodium gluconate 0.2 parts Water 79.3 parts.

[0141] Ink composition of EXAMPLE 18: C.I. Direct Blue 199 3 parts Glycerol 5 parts Ethylene glycol 10 parts 2-Propanol 3 parts Sodium gluconate 0.5 parts Water 78.5 parts.

[0142] Ink composition of EXAMPLE 19: Projet Fast Black 2 (product of 2 parts Zeneca Co.) Glycerol 5 parts Diethylene glycol 5 parts Urea 4 parts 2-Propanol 3.5 parts Sodium gluconate 10 parts Sodium hydroxide 0.1 parts Ammonium sulfate 0.1 parts Water 70.3 parts.

EXAMPLE 20

[0143] (Preparation of Pigment Dispersion 1) Styrene-acrylic acid-butyl acrylate 5   parts terpolymer (acid value: 115;, average molecular weight: 3,700) Triethanolamine 0.5 parts Diethylene glycol 5   parts Water 69.5 parts.

[0144] The above components were mixed, and the mixture was heated to 70° C. in a water bath, thereby completely dissolving the resin component. To this solution, were added 15 parts of carbon black (“MA-100”, trade name; pH: 3.5; product of Mitsubishi Kagaku Co., Ltd.) and 5 parts of 2-propanol to premix the components for 30 minutes. Thereafter, the resultant premix was subjected to a dispersion treatment under the following conditions.

[0145] Dispersing machine: sand grinder (manufactured by Igarashi Kikai K. K.)

[0146] Grinding medium: zirconium beads (diameter: 1 mm)

[0147] Packing rate of grinding medium: 50% (by volume)

[0148] Grinding time: 3 hours.

[0149] The thus-treated mixture was further subjected to a centrifugal treatment (12,000 rpm, 20 minutes) to remove coarse particles, thereby obtaining Pigment Dispersion 1.

[0150] (Preparation of Ink of Example 20)

[0151] The following components were mixed in a beaker and stirred at 25° C. for 3 hours to prepare an ink of EXAMPLE 20 used in the present invention. Pigment Dispersion 1 30 parts Diethylene glycol 10 parts 2-Propanol 2 parts Sodium gluconate 1 part Water 57 parts.

EXAMPLE 21

[0152] (Preparation of Pigment Dispersion 2)

[0153] After 300 g of commercially-available acid carbon black (“MA77”, trade name; pH: 3.0; product of Mitsubishi Kagaku Co., Ltd.) were thoroughly mixed with 1,000 ml of water, 450 g of sodium hypochlorite (available chlorine concentration: 12%) were added dropwise to the mixture, followed by stirring for 10 hours at 100 to 105° C. The resultant slurry was filtered through Toyo Filter Paper No. 2 (product of Advantes Co.) to fully wash the resultant pigment particles with water. The wet cake of this pigment was dispersed again in 3,000 ml of water, and the dispersion was desalted by means of a reverse osmosis membrane to a conductivity of 0.2 μs. The pigment dispersion (pH: 8 to 10) was concentrated to a pigment concentration of 10% by weight. The above-described process was followed to introduce a -COONa group into the surface of carbon black.

[0154] (Preparation of Ink of Example 21)

[0155] The following components were mixed in a beaker and stirred at 25° C. for 3 hours. The mixture was filtered under pressure through a membrane filter (product of Sumitomo Electric Industries, Ltd.) having a pore size of 3.0 μm to prepare an ink of EXAMPLE 21 used in the present invention. Pigment Dispersion 2 30 parts Glycerol 5 parts Trimethylolpropane 5 parts Ethylene oxide adduct of acetylene 0.2 parts glycol (Acetylenol EH, trade name, product of Kawaken Fine Chemicals Co., Ltd.) Sodium gluconate 1.0 part Water 58.8 parts.

EXAMPLE 22

[0156] (Preparation of Pigment Dispersion 3) Styrene-acrylic acid copolymer 5.5 parts (acid value: 200;, average molecular weight: 7,000) Monoethanolamine 1.0 parts Ion-exchanged water 67.5 parts Diethylene glycol 5.0 parts.

[0157] The above components were mixed, and the mixture was heated to 70° C. in a water bath, thereby completely dissolving the resin component.

[0158] To this solution, were added 20 parts of C.I. Pigment Yellow 93 and 1.0 part of isopropyl alcohol to premix the components for 30 minutes. Thereafter, the resultant premix was subjected to a dispersion treatment under the following conditions.

[0159] Dispersing machine; sand grinder

[0160] Grinding medium: glass beads (diameter: 1 mm)

[0161] Packing rate of grinding medium: 50% (by volume)

[0162] Grinding time: 3 hours.

[0163] The thus-treated mixture was further subjected to a centrifugal treatment (12,000 rpm, 20 minutes) to remove coarse particles, thereby obtaining Pigment Dispersion 3.

[0164] (Preparation of Ink of Example 22)

[0165] The following components were mixed in a beaker and stirred at 25° C. for 3 hours to prepare an ink of EXAMPLE 22 used in the present invention. Pigment Dispersion 3 20 parts Glycerol 15 parts Diethylene glycol 10 parts Acetylenol EH (trade name, product 0.3 parts of Kawaken Fine Chemicals Co., Ltd.) Sodium gluconate 1 part Water 53.7 parts.

EXAMPLE 23

[0166] Pigment Dispersion 4 was prepared in the same manner as in the preparation of Pigment Dispersion 3 except that C.I. Pigment Yellow 93 in Pigment Dispersion 3 prepared in EXAMPLE 22 was changed to C.I. Pigment Red 122.

[0167] An ink of EXAMPLE 23 was prepared in the same manner as in the preparation of the ink in EXAMPLE 22 except that Pigment Dispersion 4 was used.

EXAMPLE 24

[0168] Pigment Dispersion 5 was prepared in the same manner as in the preparation of Pigment Dispersion 3 except that C.I. Pigment Yellow 93 in Pigment Dispersion 3 prepared in EXAMPLE 22 was changed to C.I. Pigment Blue 15:3. An ink of EXAMPLE 24 was prepared in the same manner as in the preparation of the ink in EXAMPLE 22 except that Pigment Dispersion 5 was used.

Comparative Examples 5 to 18

[0169] The following respective components were mixed and thoroughly stirred into solutions. The resultant solutions were then filtered under pressure through a microfilter (product of Fuji Photo Film Co., Ltd.) having a pore size of 0.2 μm, thereby preparing inks according to COMPARATIVE EXAMPLEs 5 to 13.

[0170] Ink composition of COMPARATIVE EXAMPLE 5: Projet Fast Black 2 (product of 2 parts Zeneca Co.) Diethylene glycol 10 parts Sodium hydroxide 0.1 parts Water 87.9 parts.

[0171] Ink composition of COMPARATIVE EXAMPLE 6: Projet Fast Yellow 2 (product of 3 parts Zeneca Co.) Diethylene glycol 10 parts Water 87 parts.

[0172] Ink composition of COMPARATIVE EXAMPLE 7: Projet Fast Magenta 2 (product of 3 parts Zeneca Co.) Diethylene glycol 10 parts Water 87 parts.

[0173] Ink composition of COMPARATIVE EXAMPLE 8: Projet Fast Cyan 2 (product of 4 parts Zeneca Co.) Diethylene glycol 10 parts Water 86 parts.

[0174] Ink composition of COMPARATIVE EXAMPLE 9: C.I. Food Black 2 3 parts Glycerol 5 parts Ethylene glycol 10 parts 2-Propanol 3 parts Water 79 parts.

[0175] Ink composition of COMPARATIVE EXAMPLE 10: C.I. Acid Yellow 23 2 parts Diethylene glycol 10 parts Water 88 parts.

[0176] Ink composition of COMPARATIVE EXAMPLE 11: C.I. Reactive Red 180 3 parts Diethylene glycol 10 parts Water 87 parts.

[0177] Ink composition of COMPARATIVE EXAMPLE 12: C.I. Direct Blue 199 5 parts Diethylene glycol 10 parts Water 85 parts.

[0178] Ink composition of COMPARATIVE EXAMPLE 13: C.I. Direct Black 195 2 parts Glycerol 5 parts Diethylene glycol 5 parts Urea 5 parts Sodium hydroxide 0.1 parts Ammonium sulfate 0.1 parts Water 82.8 parts.

[0179] Ink composition of COMPARATIVE EXAMPLE 14:

[0180] The following components were mixed in a beaker and stirred at 25° C. for 3 hours to prepare an ink of COMPARATIVE EXAMPLE 14. Pigment Dispersion 1 30 parts Diethylene glycol 10 parts 2-Propanol 2 parts Water 58 parts.

[0181] Ink composition of COMPARATIVE EXAMPLE 15:

[0182] The following components were mixed in a beaker and stirred at 25° C. for 3 hours. The mixture was filtered under pressure through a membrane filter (product of Sumitomo Electric Industries, Ltd.) having a pore size of 3.0 μm to prepare an ink of COMPARATIVE EXAMPLE 15. Pigment Dispersion 2 30 parts Glycerol 5 parts Trimethylolpropane 5 parts Ethylene oxide adduct of acetylene 0.2 parts glycol (Acetylenol EH, trade name, product of Kawaken Fine Chemicals Co., Ltd.) Water 59.8 parts.

[0183] Ink composition of COMPARATIVE EXAMPLE 16:

[0184] The following components were mixed in a beaker and stirred at 25° C. for 3 hours to prepare an ink of

Comparative Example 16

[0185] Pigment Dispersion 3 20 parts Glycerol 15 parts Diethylene glycol 10 parts Acetylenol EH (trade name, product 0.3 parts of Kawaken Fine Chemicals Co., Ltd.) Water 54.7 parts.

[0186] Ink composition of COMPARATIVE EXAMPLE 17:

[0187] The following components were mixed in a beaker and stirred at 25° C. for 3 hours to prepare an ink of COMPARATIVE EXAMPLE 17. Pigment Dispersion 4 20 parts Glycerol 15 parts Diethylene glycol 10 parts Acetylenol EH (trade name, product 0.3 parts of Kawaken Fine Chemicals Co., Ltd.) Water 54.7 parts.

[0188] Ink composition of COMPARATIVE EXAMPLE 18:

[0189] The following components were mixed in a beaker and stirred at 25° C. for 3 hours to prepare an ink of COMPARATIVE EXAMPLE 18. Pigment Dispersion 5 20 parts Glycerol 15 parts Diethylene glycol 10 parts Acetylenol EH (trade name, product 0.3 parts of Kawaken Fine Chemicals Co., Ltd.) Water 54.7 parts.

[0190] [Evaluation 2]

[0191] The ink of EXAMPLEs 4 to 24 and COMPARATIVE EXAMPLEs 5 to 18 were used to conduct the following evaluation by means of an ink-jet recording apparatus having an On-Demand type multi-recording head (BC-02, trade name, manufactured by Canon Inc.; the outermost protective layer on a heater is formed of tantalum and tantalum oxide) which ejects an ink by applying thermal energy in response to recording signals to the ink. In the evaluation, Vth (critical voltage that the recording head may barely conduct ejection) was actually measured at a pulse width of 1.1 μs (On)+3.0 μs (Off)+3.2 μs (On), and a driving frequency of 6250 Hz, and the evaluation was conducted at Vop (driving voltage) corresponding to an r value of 1.39. The results are shown in Table 2.

[0192] Ejection Durability:

[0193] Continuous ejection was conducted by the above-described apparatus under the above-described respective driving conditions to collect a droplet ejected from the recording head every 1×10⁶ droplets in a container and weigh it by an electronic balance. An average quantity in 1×10⁶ droplets ejected was calculated from an increment in the weight of the container. The Continuous ejection was conducted up to 1×10⁸ droplets to conduct the evaluation in accordance with the following standard.

[0194] A: An average quantity of droplets ejected between the 9.9×10⁷-th droplet and the 1×10⁸-th droplet was at least 90% of an average quantity of droplets ejected between 0 to 1×10⁶-th droplet;

[0195] B: An average quantity of droplets ejected between the 9.9×10⁷-th droplet and the 1×10⁸-th droplet was not lower than 70%, but lower than 90% of an average quantity of droplets ejected between 0 to 1×10⁶-th droplet;

[0196] C: An average quantity of droplets ejected between the 9.9×10⁷-th droplet and the 1×10⁸-th droplet was lower than 70% of an average quantity of droplets ejected between 0 to 1×10⁶-th droplet;

[0197] D: Led into a failure to eject in the course

[0198] Degree of Kogation:

[0199] The recording head of the recording apparatus used in the ejection durability test was disassembled after completion of the evaluation to observe the surface of the heater in the nozzle used in the ejection durability test through an optical microscope (400 magnifications), thereby evaluating the degree of kogation in accordance with the following standard:

[0200] A: Kogation was scarcely observed;

[0201] B: Kogation was slightly observed, but no practical problem was caused;

[0202] C: Kogation was observed to a great extent;

[0203] D: Kogation was observed to a very great extent. TABLE 2 Coloring Vth Vop Ejection Degree of Type of aldonic acid material (V) r value (V) durability kogation Ex. 4 Sodium gluconate Projet Fast Black 20.9 1.39 24.6 A A 3 parts 2, 2 parts Ex. 5 40% aq. DL-glyceric Projet Fast Black 20.8 1.39 24.5 A A acid, 4 parts 2, 2 parts Ex. 6 D-Erythronolactone Projet Fast Black 21.0 1.39 24.8 A A 2 parts 2, 2 parts Ex. 7 δ-Ribonolactone Projet Fast Black 21.0 1.39 24.8 A A 2 parts 2, 2 parts Ex. 8 γ-D-Galactono- Projet Fast Black 21.2 1.39 25.0 A A lactone 2 parts 2, 2 parts Ex. 9 δ-Gluconolactone Projet Fast Black 21.5 1.39 25.3 A A 2 parts 2, 2 parts Ex. 10 50% aq. gluconic Projet Fast Black 21.0 1.39 24.8 A A acid, 4 parts 2, 2 parts Ex. 11 Sodium gluco- Projet Fast Black 20.9 1.39 24.6 A A heptonate 2 parts 2, 2 parts Ex. 12 Sodium gluconate Projet Fast 21.3 1.39 25.1 A A 2 parts Yellow 2, 3 parts Ex. 13 Sodium gluconate Projet Fast 21.0 1.39 24.8 A A 2 parts Magenta 2, 3 parts Ex. 14 Sodium gluconate Projet Fast Cyan 21.0 1.39 24.8 A A 2 parts 2, 4 parts Ex. 15 Sodium gluconate C.I. Food Black 2, 20.9 1.39 24.6 A A 0.5 parts 2 parts Ex. 16 Sodium gluconate C.I. Acid Yellow 21.0 1.39 24.8 A A 0.1 parts 23, 2 parts Ex. 17 Sodium gluconate C.I. Reactive Red 21.0 1.39 24.8 A A 0.2 parts 180, 2.5 parts Ex. 18 Sodium gluconate C.I. Direct Blue 21.3 1.39 25.1 A A 0.5 parts 199, 3 parts Ex. 19 Sodium gluconate Projet Fast Black 21.0 1.39 24.8 A A 10 parts 2, 2 parts Ex. 20 Sodium gluconate Carbon black, 21.0 1.39 24.8 A A 1 part 4.5 parts Ex. 21 Sodium gluconate Carbon black 21.0 1.39 24.8 A A 2 parts (COONa group was introduced), 3 parts Ex. 22 Sodium gluconate C.I. Pigment 21.5 1.39 25.3 A A 1 part Yellow 93, 4 parts Ex. 23 Sodium gluconate C.I. Pigment Red 21.0 1.39 24.8 A A 1 part 122, 4 parts Ex. 24 Sodium gluconate C.I. Pigment Blue 21.0 1.39 24.85 A A 1 part 15:3, 4 parts Comp. Not added Projet Fast Black 20.9 1.39 24.6 C C Ex. 5 2, 2 parts Comp. Not added Projet Fast 20.7 1.39 24.4 B B Ex. 6 Yellow 2, 3 parts Comp. Not added Projet Fast 21.3 1.39 25.1 C C Ex. 7 Magenta 2, 3 parts Comp. Not added Projet Fast Cyan 21.0 1.39 24.8 B B Ex. 8 2, 4 parts Comp. Not added C.I. Food Black 2, 20.6 1.39 24.3 B B Ex. 9 2 parts Comp. Not added C.I. Acid Yellow 21.3 1.39 25.1 B B Ex. 10 23, 2 parts Comp. Not added C.I. Reactive Red 21.0 1.39 24.8 B B Ex. 11 180, 2.5 parts Comp. Not added C.I. Direct Blue 21.0 1.39 24.8 B B Ex. 12 199, 3 parts Comp. Not added Projet Fast Black 21.1 1.39 24.9 C C Ex. 13 2, 2 parts Comp. Not added Carbon black, 21.2 1.39 25.0 C C Ex. 14 4.5 parts Comp. Not added Carbon black 21.5 1.39 25.3 B B Ex. 15 (COONa group was introduced), 3 parts Comp. Not added C.I. Pigment 21.2 1.39 25.0 B C Ex. 16 Yellow 93, 4 parts Comp. Not added C.I. Pigment Red 21.0 1.39 24.8 B C Ex. 17 122, 4 parts Comp. Not added C.I. Pigment Blue 21.1 1.39 24.9 B C Ex. 18 15:3, 4 parts 

What is claimed is:
 1. A method of reducing kogation on the surface of a heater for applying thermal energy to an ink to eject the ink from an orifice in an ink-jet printer having a recording head equipped with said heater, wherein said heater has an outermost protective layer comprising a metal and/or a metal oxide, and said ink comprises (a) a coloring material, (b) a liquid medium, and (c) at least one selected from the group consisting of aldonic acid, γ-aldonolactone, δ-aldonolactone and aldonates.
 2. The method according to claim 1, wherein said metal and/or said metal oxide is tantalum and/or tantalum oxide.
 3. The method according to claim 1, wherein the energy Eop applied to said heater for ejecting said ink meets the relationship 1.10≦Eop/Eth≦1.50 wherein Eth is a threshold quantity of energy applied to said heater, which is required to eject said ink.
 4. The method according to any one of claims 1 to 3, wherein at least one selected from said group consisting of aldonic acid, γ-aldonolactone, δ-aldonolactone and aldonates is at least one selected from the group consisting of gluconic acid, γ-gluconolactone, δ-gluconolactone and gluconate.
 5. The method according to claim 4, wherein said gluconate are selected from the group consisting of lithium gluconate, sodium gluconate and potassium gluconate.
 6. The method according to claim 1, wherein said coloring material is a water-soluble dye.
 7. The method according to claim 1, wherein said coloring material is a pigment.
 8. The method according to claim 1, wherein the content of water in said ink is 35 to 96% by weight based on the total weight of said ink.
 9. An ink-jet recording process comprising the step of applying thermal energy to an ink to eject the ink from an orifice, wherein said ink comprises (a) a coloring material, (b) a liquid medium, and (c) at least one selected from the group consisting of aldonic acid, γ-aldonolactone, δ-aldonolactone and aldonates.
 10. An ink-jet recording apparatus comprising: an ink container portion containing an ink, an ink-jet recording head having a heater for applying thermal energy to said ink within an ink flow path, said ink being fed from said ink container portion, and a means for applying a pulsed electric signal in response to recording information to said heater, wherein said heater has an outermost protective layer comprising a metal and/or a metal oxide, and said ink comprises (a) a coloring material, (b) a liquid medium, and (c) at least one selected from the group consisting of aldonic acid, γ-aldonolactone, δ-aldonolactone and aldonates.
 11. The ink-jet recording apparatus according to claim 10, wherein said heater has a outermost protective layer comprising at least one of a metal and a metal oxide.
 12. The ink-jet recording apparatus according to claim 11, wherein said metal is tantalum.
 13. The ink-jet recording apparatus according to claim 11, wherein said metal oxide is tantalum oxide.
 14. The ink-jet recording apparatus according to claim 10, wherein the energy Eop applied to said heater by said means for applying a pulsed electric signal in response to recording information meets the relationship 1.10≦Eop/Eth≦1.50 wherein Eth is a threshold quantity of energy applied to said heater, which is required to eject said ink.
 15. A recording unit comprising an ink container portion containing an ink, and an ink-jet recording head for ejecting said ink from an orifice by the action of thermal energy, wherein said ink-jet recording head is equipped with a heater for applying thermal energy to said ink, said heater having an outermost protective layer comprising a metal and/or a metal oxide, and said ink comprises (a) a coloring material, (b) a liquid medium, and (c) at least one selected from the group consisting of aldonic acid, γ-aldonolactone, δ-aldonolactone and aldonates.
 16. The recording unit according to claim 15, wherein said metal is tantalum.
 17. The recording unit according to claim 15, wherein said metal oxide is tantalum oxide.
 18. method of lengthening the life of a recording head equipped with a heater for applying thermal energy to an ink, said recording head being used for an ink-jet recording process including the step of applying thermal energy to said ink to eject the ink from an orifice, comprising the steps of providing an outermost protective layer containing at least one of a metal and a metal oxide on said heater, and using, as said ink, an ink containing (a) a coloring material, (b) a liquid medium, and (c) at least one selected from the group consisting of aldonic acid, γ-aldonolactone, δ-aldonolactone and aldonates.
 19. The process according to claim 18, wherein said metal is tantalum.
 20. The process according to claim 18, wherein said metal oxide is tantalum oxide.
 21. The process according to any one of claims 18 to 20, wherein the energy Eop applied to said heater for generating thermal energy applied to said ink meets the relationship 1.10≦Eop/Eth≦1.50 wherein Eth is a threshold quantity of energy applied to said heater, which is required to eject said ink. 